(1) Field of the Invention
The present invention relates to a rolling bearing for linear motion wherein a slide unit is mounted on a track rail with, track plates having track surfaces facing track surfaces on both sides of the track being fitted symmetrically left and right at channel shaped inside surfaces of said slide unit and the slide unit is capable of making a linear motion against the track rail through rolling bodies mounted between the track surface of said track plate and the track surface of said track rail.
The present invention also relates to an improvement of a rolling bearing for linear motion comprising particularly a track rail provided with linear tracks symmetrically at left and right and a slide unit which is mounted on said track rail which accommodates a group of balls so that said balls roll endlessly along the tracks of said track rail.
(2) Explanation of Prior Art
One example of prior art rolling bearing for linear motion is shown in U.S. Pat. No. 3,938,854 specification. As shown in FIG. 6, the outline is as follows:
A slide unit 102, which is mounted on a track rail 101, is supported by 4 sets of tracks provided by an upper, lower, left and right portions of the track rail 101 and by balls 103, and performs a linear motion in the axial direction of the track rail 101. Radial loads in any direction perpendicular to the axis and moment loads imposed on the slide unit 102 are supported by 4 sets of group of balls.
In this prior art example, since 4 sets of upper, lower, left and right group of balls are installed, there were such disadvantages that, the overall construction of the rolling bearing for linear motion became complicated, the height of the section was increased, the number of machining operations increased resulting in high cost. Also, in particular, the 4 sets of ball groups were disposed in such a manner that the downward load was higher than the upward load.
As another prior art example there was one as shown in FIG. 7. In this example, the opposing surfaces of track rail 201 and slide unit 202 are made trapezoidal, with the upward, downward, left and right direction radial load and moment loads supported by the tracks and a group of balls 203 provided one set each at the left and the right slanted surfaces.
In this prior art example, since the track surface is provided at the slanted surface of a trapezoidal, there were disadvantages as, the height of the cross section was high, and an upward load capacity which supports the upward load was too small to be practical enough.
As shown in FIG. 8, in both of the previously described prior art examples, the contact and support force relation between track rail 301 and slide unit 302 was such that the contact positions between respective track surfaces 304, 305 and ball 303 were in 45.degree. symmetry, as shown by arrows E, F, G, H, to opposing surface 306 of the track rail 301 and opposing surface 307 of the slide unit 302.
In both of the above prior art examples, since the height and width of the track rail 301 and the slide unit 302 become large, if installed on a slide surface of various equipment for a bearing for linear motion, the variety of equipment will become large for the sole reason of the configuration of the bearing, and thus there was a great demand for making the bearing compact.
Also in the above second prior art example, there was a demand to increase the upward load capacity.
Further, in a third prior art example as disclosed by U.S. Pat. No. 2,994,567 specification, as shown in FIG. 9, a slide unit 402 makes a linear motion on a track rail 401 through left and right groups of balls 403 which are retained freely for rolling in retainer 44 for left and right. However, in this case, the upper, lower, left and right four contact points between the ball group 403 and track surfaces of the track rail 402 and slide unit 402 are made in 45.degree. symmetry left and right to the vertical surface, and thus the upward load capacity and downward load capacity are the same. Since the downward load capacity is not larger than the upward load capacity as is required in the normal state of use, if downward load capacity is increased by increasing the size of the construction, it will result in an increase of upward load capacity, and thus there is a disadvantage of unnecessarily increasing to a larger constructional size. Thus, there was a demand to increase the downward load capacity only without increasing the unnecessary upward load capacity and prevent the size from becoming large.
Further, in the prior art preload device for preloading the track plate 9 having the track surface 5 of the slide unit 2 of the rolling bearing for linear motion, as shown in FIG. 12, the track plate 9 is placed and fitted at inside surface 7 of slide unit main body 15 which faces the track surface 4 of side surface 6 of the track rail 1, and the construction is made so that at least one side of the surfaces of said track surface 9 (in the drawing, right side) is directly contacted by the end of a preload bolt 19 which is screwed in to advance or retract against the track plate 9 from the outer surface 10 of said slide unit main body 15, and thus is arranged to preadjust the preload force to be imposed on the rolling body which is ball 3 mounted between said both track surfaces 4, 5 and on said both track surfaces.
However, in this preload device, since the portion of pressure contact made on the track plate 9 is a small area of an end of a preload bolt, the preload force produced by the tightening force of the preload bolt 19 was not necessarily uniformly transmitted to the track surface 9, and frequently uneven forces were imposed on the track surface 9 and the advancing or retracting sliding of the track surface 9 was not smooth, and also since the contact area between the preload bolt 19 and track surface 9 was small, a large preload force could not be imposed. Therefore, a preload device without these disadvantages was desired.